U.S. Ambassador Ryan Crocker half jokes that his long-term planning in Iraq runs roughly two weeks ahead of him. "Almost anything is possible here," said Crocker, speaking at a "farewell" session with reporters in Baghdad. "You cannot underestimate the challenges and the time it takes to work through them." Crocker, who plans to step down as ambassador and retire in about three weeks, was sounding a note of caution on the prospects for Iraq in the aftermath of what appears to be pressure for an even speedier U.S. withdrawal of forces.

According to a recently signed agreement between the U.S. and Iraq, American forces are to be off the streets of Iraq by this summer and gone entirely from the country by 2011. During his campaign, however, Barack Obama pledged to withdraw all combat forces from Iraq within 16 months of taking office  which would be May 20, 2010  and so far has not publicly backed away from that promise. Indeed, as Obama prepared to meet with Pentagon officials yesterday, his spokesman Robert Gibbs said, "He will ask for planning to redeploy combat troops within 16 months." Senior officials in Iraq are making clear that they too are open to seeing U.S. troops depart ahead of schedule, setting the stage for a renegotiated U.S.-withdrawal deadline (See pictures of how Iraq's street are returning to normal.)

But not everyone in Iraq is eager to speed things up. Crocker and senior U.S. military officials in Iraq have repeatedly warned that reducing troops too quickly risks renewing sectarian violence, which has fallen to its lowest levels since the U.S. invasion in 2003. The ambassador stressed the point again, saying insurgent forces in Iraq remained deadly and poised to reassert themselves. Moreover, Crocker said, a hasty departure of U.S. forces might deepen doubt among Iraqis, who tend to see the current security gains as fragile. "I think it would have a chilling effect on Iraqis," Crocker said.

Crocker is not the only one in Baghdad concerned about emerging plans for a speedier U.S. withdrawal. General Baha'a Nouri Yasseen, a commander of the National Police in Baghdad, said U.S. forces needed to stay for the time being. "Personally, I hope the Americans don't leave now," Yasseen told TIME. "It's not the right time."

Insurgent activity persists in eastern and northern Iraq, and almost every day Baghdad still shakes with bomb explosions. Whether this lingering violence will rise as U.S. forces pull out remains the great unknown. Iraqi security forces are more numerous and stronger than they have been since the U.S. military started building them up roughly six years ago, and they may be able to hold back the lingering insurgent movement. Or not.

What remains of the insurgency may gain new life if disaffected political elements on the losing end of the coming provincial elections Jan. 31 turn toward violence. And militias remain a lurking presence in the political process as well. The truth is that any move by the new White House on a U.S. withdrawal is a gamble, including sticking to the current timetable. Even the sharpest of Iraq observers have failed to foresee key turns for the better and worse over the years.